1. Field of the Invention
The present invention relates to an image converter circuit for converting the horizontal/vertical number of pixels of an input image into the number of pixels of a display device, and more particularly to an image converter circuit for panoramically displaying, without image deterioration, the input-image data having a small aspect ratio (e.g., 4:3) on a display device having a larger aspect ratio (e.g., 16:9).
2. Description of the Related Art
FIG. 1 is a configuration diagram of a conventional image converter circuit. The conventional image converter circuit has a data input section 1 to which is provided input-image data IN having an aspect ratio of 4:3, e.g., 720 horizontal pixels×540 vertical pixels, and has an image memory 2 connected to the data input section 1. The image memory 2 is constituted by 540 line memories for storing 720 pixels of image data of each of 540 horizontal lines. The input-image data IN inputted through the data input section 1 is sequentially written into the image memory 2.
The image memory 2 is connected to a read control section 3. The read control section 3 reads the designated image data from the image memory 2 in accordance with read-designating information READ designating the position of a pixel to be converted, and provides it to a data interpolating section 4. The data interpolating section 4 enlarges the image data provided from the read control section 3 by interpolating pixels depending upon magnification-designating information MULT, and outputs the enlarged image data OUT.
The image converter circuit has a conversion-control section 5 that sequentially generates, in predetermined timing, signals representing read-designating information READ and magnification-designating information MULT in synchronization with a clock signal CLK, and provides those signals to the read-control section 3 and the data interpolating section 4. The conversion-control section 5 is connected to both a fixed-magnification setting section 7 and a panoramic-magnification setting section 8, through a selector 6 that switches a display mode in response to a mode signal MOD.
The fixed-magnification setting section 7 designates a magnification (horizontally 4/3 times) at which the input-image data IN having 720 horizontal pixels×540 vertical pixels is uniformly enlarged for display on a display device having an aspect ratio of 16:9, e.g., 960 horizontal pixels×540 vertical pixels.
On the other hand, in order to generate a panoramic image, the panoramic-magnification setting section 8 vertically divides the screen into a certain number of blocks and takes a low magnification (e.g. 1 times) for the central block, a high magnification (e.g. 2 times) for the outer blocks, and an intermediate magnification changing in incremental steps for the intermediate blocks.
The fixed-magnification setting section 7 and the panoramic-magnification setting section 8 are configured by a ROM (read-only memory) stored with magnifications that is in advance calculated on a block-by-block basis in accordance with both the number of pixels of the input-image data IN provided from an applicable device and the number of pixels of a display device.
Explanation will now be made on the operation of the conventional image converter circuit.
For example, when digitized input-image data IN is provided from a video decoder of a not-shown television receiver, the input-image data IN is sequentially written on a line-by-line basis into the image memory 2 by a data-input section 1.
In this case, when a fixed-magnification display mode is set, the selector 6 selects the fixed-magnification setting section 7 so that the fixed-magnification information representing about 4/3 times stored in the ROM of the fixed-magnification setting section 7 is provided to the conversion-control section 5. Thus, the fixed-magnification information representing about 4/3 times is provided from the conversion-control section 5 to the data interpolating section 4. Then, the conversion-control section 5 outputs read-designating information READ to the read-control section 3 thereby to read the beginning four pixels from the image memory 2. This causes the read-control section 3 to read the beginning four pixels from the image memory 2 and provides those to the data interpolating section 4.
In the data interpolating section 4, three segments defined by the four pixels are re-defined into four segments, to calculate values (i.e., intensity levels) on the three pixels at boundaries of between the segments through linear interpolation depending upon the four-pixel values provided from the read-control section 3. The data interpolating section 4 outputs, as enlarged-image data OUT, a value of the beginning pixel, a value of the intermediate three pixels calculated and a value of the last pixel. Such operations are performed for all the pixels of each line, thereby obtaining enlarged-image data OUT to uniformly and horizontally perform an enlargement at 4/3 times.
On the other hand, when a panoramic-display mode is set, the selector 6 selects the panoramic-magnification setting section 8 to provide, to the conversion-control section 5, the panoramic-magnification information stored in the ROM of the panoramic-magnification setting section 8.
A panoramic magnification as an enlargement ratio is set for each of the blocks obtained by vertically dividing the screen. Thus, the selector 6 switches information in order between the read-designating information READ provided from the conversion-control section 5 to the read-control section 3, and the magnification-designating information MULT provided to the data interpolating section 4, on every block for read and conversion.
For example, for converting the blocks on the left and right ends of the screen, magnification-designating information MULT is given as two times while read-designating information READ is as the horizontal number of pixels of the block at the end. Meanwhile, for converting the block at the center block of the screen, magnification-designating information MULT is given as one times while read-designating information READ is as the number of pixels of the central block.
In the data interpolating section 4, linear interpolation is performed to make the pixels provided from the read-control section 3 into the number corresponding to the magnification given by the magnification-designating information MULT. Those are enlarged to the magnification designated for each of the blocks, thus being outputted as enlarged-image data OUT. This provides enlarged-image data OUT that enlargement is horizontally done to the panoramic magnification.
Incidentally, in the present example, because the vertical number of pixels on the screen is equal between input and output, enlargement-interpolation is not done vertically. Where the vertical number of pixels is different between input and output, enlargement-interpolation is performed at a fixed magnification.
Japanese Patent Application Publication (Kokai) No. Heill-73154 discloses a conventional image conversion device that is capable of converting the number of horizontal pixels or vertical pixels, which is incorporated herein by reference.
However, the conventional image converter circuit involves the following problem.
Namely, the fixed-magnification setting section 7 and the panoramic-magnification setting section 8 are configured by a ROM storing a value that is in advance calculated as matched to the number of pixels of input-image data IN from an applied device and to the number of pixels of the display device. For this reason, when the conventional image converter circuit is applied to a display device having the different number of output pixels for display, there encounters a case that input-image data IN cannot be displayed at its end portion or a case that there is a surplus at the end portion of the display screen. Therefore, the enlarged image cannot be appropriately displayed.
Furthermore, in the panoramic display, because of incapability of providing the large number of the blocks into which the screen can be divided, there encounters a great change of the magnification between the blocks. With displaying such a moving image that moves horizontally, there is a problem in that the moving looks unnatural and unsuitable at the boundary between the blocks.